Patent Document 1 discloses an electronic endoscope system that acquires, as endoscope observation images, normal observation images captured using normal light, and narrow-band observation images captured using narrow-band light having a bandwidth narrower than that of normal light, and displays the endoscope observation images.
Patent Document 2 discloses an image processing apparatus and an image processing method for executing image noise reduction processing using a technology called ε filter. The ε filter technology is used to perform noise reduction processing on a pixel of interest, by setting a pixel of interest and neighboring pixels out of a plurality of pixels that constitute an image, and perform averaging using only a portion in which the difference in pixel value between the pixel of interest and each neighboring pixel is smaller than or equal to a reference threshold value, while leaving a high-frequency component in which the difference in pixel value between the pixel of interest and each neighboring pixel is greater than a reference threshold value.